1. Field of the Invention
The present invention relates to a surface mount type push switch used in input operation sections of various electronic apparatuses.
2. Background Art
Recently, various electronic apparatuses typified by mobile phones have been reduced in size and thickness. Accordingly, surface mount type push switches used in input operation sections of such electronic apparatuses are also thinned. Specifically, a push switch having a configuration in which a switch main body is inserted in a cut-away portion provided in a printed circuit board so as to suppress protrusion from the surface of the printed circuit board is used.
A conventional push switch is described with reference to FIGS. 9 to 13. FIG. 9 is an outline view of a conventional push switch seen obliquely from above. FIG. 10 is an exploded perspective view of this push switch. FIG. 11 is an outline view of this push switch seen obliquely from below. FIG. 12 is a sectional view of this push switch. FIG. 13 is a sectional view showing a state in which this push switch operates.
Switch case 1 has a substantially rectangular shape having a concave portion that opens upward in the center part, and corner protruding portions 1A at the four corners. Furthermore, switch case 1 has center contact 2 in the center of the inner bottom surface of the concave portion and outer contacts 3 in two positions symmetrical with respect to center contact 2 (FIG. 10 shows only one outer contact 3). Terminals 2A and 3A are produced integrally with switch case 1 by insert molding. Terminal 2A is connected to center contact 2, and terminal 3A is connected to outer contact 3. Terminals 2A and 3A are led out horizontally outward from the positions at middle height on the right and left side surfaces of switch case 1.
Movable contact 4 is made of an elastic thin metal plate having an upward curved dome shape, and contained in a concave portion of switch case 1. The bottom end of the outer periphery of movable contact 4 is placed on outer contacts 3 located in two positions, and the lower surface of a dome-shaped center part of movable contact 4 faces center contact 2 with a predetermined gap.
Protective sheet 5 made of an insulating film is attached from the upper side of movable contact 4 so as to cover the concave portion of switch case 1, and movable contact 4 is contained in the concave portion. An adhesive agent (not shown) is applied to the lower surface of protective sheet 5.
Operation body 6 includes operation part 6A protruding to the front side of switch case 1, elastic rod-shaped pushing part 6B in the rear side of operation part 6A, and frame part 6C surrounding pushing part 6B. Four corner protruding portions 1A of switch case 1 guide operation body 6, so that operation body 6 can move backward and forward on the top surface of protective sheet 5.
Substantially rectangular cover 7 has tilting part 7A, which is bent obliquely downward, in the center part thereof. Cover 7 is combined with switch case 1 from the upper side of operation body 6. Locking parts 7B formed by being bent downward from four corners of cover 7 are locked and fixed to locking protrusions 1B provided on corner protruding portions 1A of switch case 1.
Pressing part 6B has a spherical tip and is brought into contact with tilting part 7A of cover 7. Pressing part 6B is located above the center part of movable contact 4 via protective sheet 5.
A conventional push switch is configured as mentioned above. Next, an operation of the push switch is described.
In FIG. 12, when a pushing force is applied to operation part 6A in a direction of arrow 60, a tip of pushing part 6B moves on protective sheet 5 while it bends obliquely downward along tilting part 7A of cover 7. According to the movement, pushing part 6B pushes the dome-shaped center part of movable contact 4 via protective sheet 5. When the pushing force is beyond a predetermined pushing force, as shown in FIG. 13, the center part of movable contact 4 is elastically deformed in a downward convex form with a click feeling, and is brought into contact with center contact 2. As a result, outer contacts 3 and center contact 2 make an electric connection with each other via movable contact 4, thus allowing terminal 2A and terminal 3A to be electrically connected to each other. Then, frame part 6C of operation body 6 is brought into contact with corner protruding portion 1A located in the rear side of switch case 1, and the backward movement of operation body 6 is restricted.
When the pushing force applied to operation part 6A is released, the center part of movable contact 4 elastically returns back to its original upward curved shape by an elastic force of itself with a click feeling, and the center part of movable contact 4 is separated from center contact 2. A returning force of movable contact 4 and an elastic force of pushing part 6B itself of operation body 6 allow the tip of pushing part 6B to move obliquely upward along tilting part 7A of cover 7. Then, operation body 6 is returned to the front side, thus electrically disconnecting between terminal 2A and terminal 3A.
The following is a description of a state in which a push switch is mounted on a printed circuit board of an electronic apparatus. FIG. 14 is an outline view showing a state in which the conventional push switch is mounted on a printed circuit board.
A plurality of lands 53 are provided on the top surface of printed circuit board 51 corresponding to the positions to which terminals 2A and 3A of the push switch are soldered. Wiring board 51 is provided with U-shaped cut-away portion 52. The width dimension and the depth dimension of U-shaped cut-away portion 52 are slightly larger than those of switch case 1 of the push switch.
In switch case 1, a part that is lower than the positions from which terminals 2A and 3A are led out is inserted in cut-away portion 52. Terminals 2A and 3A are placed on corresponding lands 53 and mounted by soldering. Operation part 6A of operation body 6 protrudes to the front side from the end part of printed circuit board 51, and it can be pushed in the direction parallel to the top surface of printed circuit board 51.
However, in the above-mentioned conventional push switch, when the push switch is mounted by soldering on printed circuit board 51, flux may spread from terminals 2A and 3A to the surface of switch case 1. When the flux reaches the ridge line of the external corner portion of switch case 1, it may spread along the ridge line and reach operation body 6, which may hinder the operation of the switch.